Evaluation And Improvement Of Carbonation Durability For Concrete Bridges

Reinforced concrete bridge has been widely used in the construction of small and medium span bridges because of its advantages of low cost,high applicability,good integrity and high bearing capacity.However,the reinforced concrete bridge beam in actual operation is prone to environmental carbonization erosion.With the increase of service time of the bridge,the depth of carbonization will gradually increase,resulting in the corrosion of reinforcing bars and the cracking of cover concrete.This phenomenon is more serious in dry-wet alternation environment,which if not treated in time will lead to the degradation of the bond strength between reinforcement and concrete and the decrease of the effective area of stress of reinforcement.As a result,the bearing capacity and durability of the bridge will be reduced,thus affecting the safety of the bridge.Therefore,it is of great significance to study the carbonation durability of concrete bridge under dry-wet alternation environment.Supported by ministry of transport construction technology projects “Research on durability evaluation method of in-service concrete beam bridge based on reliability theory”(2015 318 814 190)and Yunnan provincial transportation department science and technology project “Durability evaluation and improvement technology of existing highway structures”,the evaluation method and the improvement technology of carbonation durability for concrete bridge under dry-wet alternation environment are studied in this paper.The details and conclusions of this study are as follows:(1)Based on the field investigation of Xiaomo road,the durability disease characterization,detection index and method of bridge components in dry-wet alternation environment and atmospheric environment are determined.The statistical characteristics of concrete cover thickness,concrete strength and carbonation coefficient are determined through the statistical analysis.Based on the measured data of the bridge along Xiaomo Road and the bridge in the southern region,an analytical model for predicting the depth of carbonization is developed in terms of the concrete strength considering the influence of dry-wet alternation.(2)Providing different dry-wet alternation and carbonization systems,the general atmosphere,the high temperature solarization environment,the water changing environment,and the dry-wet alternation environment were simulated for the bridge components in the laboratory.Then the experiments were carried out to study the carbonation performance of concrete,the carbonation resistance of concrete treated with permeable coating,the penetration depth of the coating and the water absorption performance of the concrete after coating treatment.The results show that the carbonization of concrete is greatly influenced by the dry-wet alternation environment.The carbonization speed of concrete is the fastest under the dry and carbonization system,and the slowest under the soaking and carbonization system.The carbonization depth decreases with the decrease of the dry wet ratio.Silane is suitable for the protection from the general atmospheric environment and the high temperature solarization environment.In the fluctuating water level environment,the carbonization depth of concrete increases after silane treatment.Cementitious capillary crystalline waterproofing coating is suitable for the protection from the general atmospheric environment,the high temperature solarization environment and the fluctuating water level environment.The concrete with frequent contact with water has the best carbonation resistance.With the decrease of dry wet ratio,the carbonation effects of silane and cementitious capillary crystalline waterproofing coating are both improved.(3)The methods for the prediction and evaluation of durability life of bridges are established.The durability reliability index of bridges in the environment of the Xiaomo road and southern area is analyzed.In general atmosphere and dry-wet alternation environment,the durability reliability index of each component are all high.The deterioration rate of reliability index of concrete carbonization decreases after surface treated with permeable coating.The durability life of bridges in service is evaluated,and adopting permeable coating protection measures to enhance the durability of concrete bridges has good effect.